It's critically important that the local proxy process should not

inherit _our_ ends of its I/O pipes! Otherwise, closing our copy of
those handles does not cause it to see EOF on its stdin, because
it's holding the pipe open itself.

git-svn-id: svn://svn.tartarus.org/sgt/putty@6808 cda61777-01e9-0310-a592-d414129be87e